Recent years have seen a dramatic increase in monetary losses from hurricanes along the U.S. coastline. The vast majority of the damage resulted from major hurricanes (Category 3-5), with 2005’s Katrina, Rita, and Wilma producing an estimated $60 billion in insured losses alone (Insurance Information Institute, 2008). In light of these record damages, it is crucial to have a better understanding of the atmospheric and oceanic conditions that produce the most powerful hurricanes.

Prior research has focused on interseasonal variability in tropical cyclones, but much less attention has been devoted to intraseasonal variability. Maloney and Hartmann (2000a) showed that hurricanes are four times more likely to form in the western Atlantic and Gulf of Mexico when the Madden-Julian Oscillation (MJO) is in its "enhanced convection" phase. This study follows the work of Maloney and Hartmann but focuses on intense tropical cyclones (Category 3-5).

Formation points of intense tropical cyclones were overlaid on plots of MJO indices extending from the western Pacific to the eastern Atlantic. For each tropical season, tropical cyclones were classified as having formed during favorable (enhanced convection), unfavorable (suppressed convection), or neutral phases of the MJO. Chi-squared testing was performed to determine the degree to which associations could be made between the MJO and tropical cyclone variability in the Western Pacific (WPAC), Eastern Pacific (EPAC), and Atlantic (ATL) basins. It was found that the MJO is not linked to overall tropical cyclone frequency variability in these three basins. However, testing did reveal some significant associations through time.

These results do not corroborate those of Maloney and Hartmann (2000a). Two key changes in methodology are the likely driving forces behind the differing results. First, this study uses an MJO index from the CPC based on 200 hPa velocity potential anomalies, while Maloney and Hartmann (2000a) used an MJO index based on 850 hPa wind anomalies. Second, the study period here is 1978 – 2006, while Maloney and Hartmann (2000a) used data from 1949 – 1997. Future research should be conducted to examine the relationship between the MJO and tropical cyclones in more detail.